Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma and gastric lymphoma. It is estimated that 30% of the adult US population is infected with the bacterium resulting in widespread gastro-intestinal disease and huge health care costs. H. pylori expresses significant urease activity which is an essential virulence factor. Recombinant urease apoenzyme is being tested as a vaccine (with the support of NIH) in human clinical trials, due in large part, because a significant fraction of this urease activity is located on the surface of the bacterium. The mechanism by which urease and HspB (a GroEL, heat shock protein homologue) become surface associated is not understood. As preliminary data for this proposal, "altruistic autolysis" was shown as the mechanism responsible for surface localization of H. pylori urease and other cytoplasmic proteins. The primary objective of this proposal is to elucidate the mechanisms by which urease becomes surface associated in H. pylori. The long term objective of this proposal is to understand the pathogenic contribution of this novel surface localization mechanism in pathogenesis by producing specific defective mutant strain(s) and testing them in animal models. Ultimately, such studies should allow development of effective therapies, including vaccines for prevention of H. pylori-associated disease. The specific aims of this proposal are: 1) Confirm and extend the investigators' observations, using molecular technology, that autolysis followed by surface-adsorption is the principle mechanism for translocation of urease onto the surface of H. pylori. 2) Confirm and extend their observations that urease and HspB are associated with the outer membrane of H. pylori in human gastric biopsies and determine whether these proteins are associated with the outer membrane of the related bacterium, H. felis, in gastric tissue from experimentally infected mice. 3) Define the pathogenic role of urease released by bacterial autolysis. 4) Elucidate the biochemical mechanisms of autolysis in H. pylori. 5) Elucidate the genetic mechanisms of autolysis in H. pylori.